I'm serious. Came out during the cold war, and gave hope for the future. First interracial kiss on American tv.

By placing the setting in the future and in space, the writers could bring controversial subjects to light in a way no other show of it's time could.

Without Star Trek, there's likely no Star Wars, no Battlestar Galactica, no X-Files, no Fringe, no Firefly.

Your post is very good and I agree with it, perhaps with the only exception that it's underrated. It was probably underrated at one point in the past, but most consider it a classic for all of the reasons you just stated. I'm not sure it's fair to call it underrated anymore.